Diplomatic sources said it will be a first opportunity to discuss the way forward with De Mistura, an Italian-Swedish diplomat with experience in Iraq and Afghanistan.
The 67-year-old former Italian deputy foreign minister was appointed last week, replacing Algerian Lakhdar Brahimi, who resigned in May after two rounds of peace talks ended in failure.
The United Nations is hoping to get the peace process back on track but it remains unclear if the road map agreed during talks in Geneva six months ago can be salvaged.
The new push comes as Assad was sworn in today for a new seven-year term. More than 170,000 people have died in the conflict since 2011.